This invention relates to the general field of exhaust systems, and more particularly to mufflers used with internal combustion engines.
Internal combustion engines generate by products of combustion often referred to as exhaust gases. Typically, for noise control the exhaust gases pass through a muffler and tailpipe before being released. Such engines and their associated exhaust systems are ubiquitous, being used to power all types of motor vehicles as well as smaller, more specialized vehicles and devices such as, for example, golf carts, ATV""s, lawn tractors, power generators, and other turf and industrial equipment.
The exhaust gases from an internal combustion engine can be very hot, for example, over 1000xc2x0 F. Such high temperatures can affect muffler components, in particular causing mufflers to wear out and require replacement faster than otherwise. Another problem is that the high exhaust temperature may cause xe2x80x9cafter bangxe2x80x9d or xe2x80x9cback firingxe2x80x9d when unburnt or semi-burnt hydrocarbons, which may be contained in the flow are ignited upon contact with hot muffler components. High exhaust temperatures therefore are a potential safety hazard.
In conventional passenger and truck motor vehicles the exhaust gases generally cool to some extent through a long exhaust pipe between the engine and muffler. In smaller vehicles the exhaust pipe is likely to be short, with correspondingly hotter exhaust gases received by the muffler. Also, since the motor compartment in smaller vehicles is more crowded, the heat emanating from a very hot muffler is more likely to have an adverse affect on the performance or durability of neighbouring components. Thus, problems of high temperature exhaust gases can be more acute in smaller vehicles and motors. In many smaller motorized device applications the muffler may be somewhat exposed. As such, the muffler, if it gets very hot, becomes a safety hazard to users of the motorized device. One solution is for such mufflers to be built with an insulated double layer outer wall. This type of muffler lowers the surface temperature of the muffler, which usefully helps prevent burns to users who may have incidental contact with the muffler and also reduces heat damage to neighbouring components. However, the outer insulation in this type of muffler also magnifies the problem of high internal and tailpipe exit temperature for the exhaust gases.
Such problems have led to a different approach, which is disclosed in U.S. Pat. No. 4,265,332 to Presnall. This patent shows a muffler surrounded by a heat shield that defines an annular air passage 68 around the outer surface of the muffler. At the tailpipe output of the muffler the heat shield narrows. When in use, the exhaust gases exiting the tailpipe pass out the muffler and through the narrow part. This draws ambient air through the air passage 68. The ambient air flow cools the body of the muffler as it contacts the muffler""s hot outer surface. The ambient air continues to flow around the muffler until it mixes with the exhaust gases to cool the exhaust gas output. Similar devices that also use an external heat shield, and that draw air through an air gap concentric to the muffler by means of a narrow venturi at the exhaust gas exit are shown in U.S. Pat. No. 4,741,411 to Stricker and U.S. Pat. No. 4,487,289 to Kicinski.
While these devices produce some cooling, the effect is limited since the cool air only passes past the outer skin of the muffler. The hot exhaust gas inside the muffler is relatively unaffected. Further, the external heat shield adds bulk to the muffler, which can be a problem particularly in smaller vehicles where the space is not available. This may force a costly redesign of the motor compartment and lead to a larger overall device. Also the external heat shield adds weight and expense to the muffler, and is not that easy to fabricate. Accordingly, in the absence of a more effective solution the durability and safety problems inherent to mufflers operating with high temperature exhaust are likely to continue.
What is desired is an exhaust muffler which overcomes one or more of the problems associated with the current devices and methods used for cooling exhaust mufflers.
Preferably, the operating temperature inside the muffler will be reduced, so that the muffler components are subjected to less heat stress and thereby achieve enhanced durability. The temperature of the exhaust gas output from the muffler will preferably also be reduced, producing a corresponding reduction in the risk of ignition of foreign materials and of back firing. It would be preferable as well if a heat shield or other bulky external device is not required, so that the muffler may be made as small as possible and thus more easily integrated into the existing motor compartments of the various internal combustion engine vehicles and devices.
Therefore, there is provided, according to a first aspect of the present invention, an exhaust gas muffler for an engine, said exhaust gas muffler having:
a) a body;
b) at least one inlet for said exhaust gas from said engine on said body;
c) a baffled chamber in said body to receive exhaust gas from said at least one exhaust gas inlet;
d) at least one exhaust gas outlet from the baffled chamber to vent said exhaust gas from said baffled chamber;
e) at least one fresh-air inlet on said body;
f) a heat exchange conduit extending into said baffled chamber between said fresh air inlet and said at least one exhaust gas outlet, said heat exchange conduit being sized and shaped to permit heat exchange between said fresh air and said exhaust gas in said baffled chamber; and
g) a fresh air outlet on said heat exchange conduit, said fresh air outlet being sized, shaped and located relative to said exhaust gas outlet to permit said fresh air to mix with exhaust gases being vented from said baffled chamber to lower an exit temperature of said exhaust gases.